Virtual Lessons

Lesson 1 of 2

Shapes of Molecules

This virtual lesson introduces electron-pair repulsion theory and applies it to predict and explain the shapes and bond angles of a range of simple molecules and ions.

The lesson opens by establishing the principles of electron-pair repulsion (VSEPR) theory, which states that electron pairs around a central atom arrange themselves to minimise repulsion, determining the overall shape of the molecule or ion. The terms bond length and bond angle are defined as the tools used to describe molecular geometry precisely.

A set of key molecules and ions are then worked through in detail, with shapes and bond angles explained for each: BeCl2 (linear, 180°), BCl3 (trigonal planar, 120°), CH4 (tetrahedral, 109.5°), NH3 (trigonal pyramidal, 107°), NH4+ (tetrahedral, 109.5°), H2O (bent, 104.5°), CO2 (linear, 180°), gaseous PCl5 (trigonal bipyramidal), SF6 (octahedral, 90°), and C2H4 (planar, 120°). The influence of lone pairs on bond angles is given particular attention throughout.

The lesson concludes by applying VSEPR theory more broadly, using the patterns established to predict the shapes and bond angles of analogous molecules and ions not explicitly covered in the examples. This develops the transferable skill of reasoning from first principles about molecular geometry.